Among standard clinical measures of binocular function, the accommodative amplitude-scaled facility (AsFac) test is the most sensitive for predicting visual discomfort symptoms. The AsFac test may be a better correlate due to its individual adjustment of the accommodative stimulus (AS) based on amplitude. Another factor that could affect stimulus demand is tonic accommodation (TA). Higher TA could put the accommodation resting state closer to the target demand, effectively reducing the AS. This study examined the relationship between AsFac test and TA in symptomatic and asymptomatic graduate students.

Methods

Visual symptoms were assessed by the Convergence Insufficiency Symptom Survey (CISS). Based on the CISS adult cut-off score of 21, the sample was divided into High (N=22) and Low (N=17) symptom groups. Assessment of binocular function was made using standard clinical procedures. TA was recorded for 2 min after 5 min of dark adaptation. From the AsFac test with the plus lens, a TA-corrected AS was calculated based on testing distance, lens power, and TA with the formula: [(100/distance in cm) - lens power - TA].

Results

Among all clinical measures, including accommodative amplitude/facility, and vergence facility (3BI/12BO), only the binocular AsFac test showed a statistically significant correlation with TA (r=0.48, p=0.004). A positive correlation was found in the high symptom group (Y=6.989+2.812*X; R2=0.435; p=0.001), but not in the low symptom group (Y=13.948+0.961*X; R2=0.169; p=0.145) (Fig 1). A similar group effect was also found in the relationship between TA-corrected AS and AsFac. A statistically significant negative correlation only existed in the high symptom group (Y=14.330-1.184*X; R2=0.336; p=0.006), not in the low symptom group (Y=16.496-0.697*X; R2=0.064; p=0.406) (Fig 2).

Conclusions

Our results suggest a possible link between AsFac test and the tonic accommodative adaptation state in graduate students with significant visual discomfort. The sensitivity of the test for predicting symptom might rely, at least partly, on this correlation. TA might be utilized as compensatory mechanism for reducing AS demand at near for this population. With lowered demand, subjects would be more efficient at performing a facility test.